The compound 1-chloro-2,6-dinitro-4-(trifluoromethyl)benzene: ##STR1## is the precursor to numerous dinitroaniline herbicides, such as trifluralin, benefin, ethalfluralin, fluchloralin, and profluralin. The compound is aminated ##STR2## to obtain the various dinitroanilines.
Because the advent of a new analytical device known as a thermal energy analyzer (TEA), it is now possible to analyze for the nitroso group at concentrations as low as 0.02 ppm -- much lower than prior analytical techniques. Analysis of various dinitroanilines by the TEA reveals that some of the dinitroanilines contain very small amounts of nitrosamine. Certain nitrosamine compounds have been shown to be carcinogenic in animals. Therefore, it is desirable to minimize nitrosamine concentrations in the dinitroanilines.
The present process provides a unique method of lowering nitrosamine concentrations in the dinitroanilines. The precursor compound, 1-chloro-2,6-dinitro-4-(trifluoromethyl)benzene, is generally prepared by nitration of the corresponding 1-chloro-4-(trifluoromethyl)benzene: ##STR3## It is now believed that the 1-chloro-2,6-dinitro-4-(trifluoromethyl)benzene, as thus produced, contains as impurities small amounts of nitrosating agents, including substances which can react to form the actual nitrosating species. It is conjectured that the nitrosating agents form nitrosamines on exposure to the amine employed in the subsequent amination step.
By lowering the concentration of nitrosating agents in 1-chloro-2,6-dinitro-4-(trifluoromethyl)benzene, the present process also reduces nitrosamine concentration in any ensuing dinitroaniline product.